Multifunctional star polymer with reactive and thermosensitive arms and fluorescently labeled core: synthesis and its protein conjugate

Abstract

A well-defined multifunctional star polymer consisting of reactive and thermoresponsive poly(N-isopropylacrylamide-co-acrolein) arms and an aluminum tris(8-hydroxyquinoline) (Alq₃)-bearing fluorescently labeled core was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using the “arm-first” method. Acrolein, a commercially available aldehyde-bearing monomer, was copolymerized with N-isopropylacrylamide (NIPAM) via RAFT technique in a controlled way to give well-defined linear trithiocarbonate terminated poly(NIPAM-co-acrolein) macro-RAFT agent. The preformed linear macro-RAFT agent was then cross-linked by a tri-vinyl Alq₃-containing cross-linker (Alq₃ cross-linker) in conjunction with N,N′-methylenebisacrylamide to give the desired reactive, thermoresponsive, and fluorescently labeled star polymer. The resultant star polymer exhibits a lower critical solution temperature at ∼29.8 °C in water, and displays intense greenish-yellow fluorescence with maximum emission peak around 520 nm in both organic solvent (i.e., THF) and water. Moreover, the highly reactive aldehyde functions in the arms of the star polymer could provide the key intermediates to conjugate biomolecules, and the conjugation with an aminooxy-functionalized BSA model protein was also demonstrated as an example of how the novel star polymer can be utilized to conjugate bioactive molecules, constructing fluorescently labeled “smart” polymer-protein conjugates.